This invention relates to an valve for injection injecting chemicals and similar liquid substances into sub-surface formations being penetrated by an oil or gas well. Such wells are commonly provided with a casing and tubing means enabling operation of tools for downhole operations. The running and installation of a chemical injection valve may occasionally be desirable in order to inject fluids into a formation, for example a scale inhibitor at the outset of water breakthrough. The chemical injection valve is then installed in the appropriate sliding sleeve door or tubing port, thereby replacing for example a so-called concentric standing valve.
In many practical situations a chemical injection valve according to the present invention may be used in an arrangement as described for example in U.S. Pat. No. 4,441,558, FIGS. 1 and 2 of which illustrate somewhat schematically known principles of downhole operations by means of a pumpdown toolstring. This US patent, however, is directed to a particular dual valve being an improvement and replacement of the formerly well known ball-type check valve.
Reference is also made to U.S. Pat. No. 3,051,243 which describes a form of flow-control device which may perform the function of a sliding sleeve door as referred to above.
In a simultaneous and copending patent application, Ser. No. 07/689,547, the present applicants are also describing novel and specific toolstring methods and equipment which advantageously can be employed when running and installing the present injection valve. Thus, the chemical injection valve is well suited for installation and operation within a horizontal or highly-deviated well without, however, being restricted to such use.